Firefighters holding line against massive California wildfire

The Rim Fire burns at night in this undated United States Forest Service handout photo near Yosemite National Park, California, released to Reuters August 30, 2013. REUTERS/Mike McMillan/U.S. Forest Service/Handout via Reuters

(Reuters) - Firefighters battling a colossal California wildfire that has eaten away at the Yosemite National Park backcountry managed overnight to largely stem the spread of the flames, authorities said on Sunday.

The fire sent heavy smoke on Saturday into the popular touristic Yosemite Valley, an area famed for towering granite rock formations, waterfalls and pine forests, obscuring views of popular landmarks on a holiday weekend at the end of the summer tourist season.

Despite footage from cameras posted on the park's website showing continued smoky conditions in the park, no further road closures within Yosemite were reported, and containment lines held steady at 40 percent.

"We have been able to hold the line. It's just trying to figure out how to wrap this thing up and put a bow around it," said fire incident spokeswoman Leslie Auriemmo, adding that there were no fresh closures in the park.

The Rim Fire had charred nearly 223,000 acres by early on Sunday, mostly in the Stanislaus National Forest which spreads out from Yosemite's western edge although the blaze has blackened about 6 percent of Yosemite's wilder backcountry.

The Yosemite Valley has been open to visitors since the fire broke out two weeks ago, but smoke began spreading to the area on Friday ahead of the Labor Day holiday weekend that in the past years has seen the park fill with visitors.

The smoke from the fire, whose footprint now exceeds the area of Dallas, was expected to at least partially clear on Sunday afternoon as winds shift, fire managers said.

Some 4 million people visit Yosemite each year, most going during the peak months of June through August. Some 620,000 normally visit the park in August alone, but due to the fire, attendance has dropped.

Close to 5,000 people are working to put out the fire, including firefighters from agencies across California and nearly 700 specially trained California prison inmates.

Among the landmarks potentially in the path of the blaze are two groves of the park's famed sequoia trees.

"We are working very hard to protect that. All the lines are in place so it doesn't go into those groves," Auriemmo said.

Firefighters have carried out controlled burns around the groves to clear away debris that could otherwise fuel a fire to such an intensity that it dangerously licks at the trees' crowns.

Lower-intensity fires, on the other hand, play a vital role in the reproductive cycle of the tough-barked sequoia, many of which bear the scars of past wildfires, by releasing the seeds from their cones and clearing the soil in which they germinate.

The blaze has edged out the 1932 Matilija wildfire in Ventura County to become the fourth-largest California wildfire on record, according to figures from the California Department of Forestry and Fire Protection.